1. Field of the Invention
The present invention generally relates to amplifiers, and also relates to noise cancellation.
2. Description of Related Art
Persons of ordinary skill in the art understand terms and basic concepts related to microelectronics that are used in this disclosure, such as “voltage,” “current,” “gain,” “impedance,” “circuit,” “network,” “cascode,” “current source,” “signal,” “PMOS (p-channel metal oxide semiconductor),” “circuit node,” “switch,” “complement,” “resistor,” “tunable resistor,” “single-ended,” “differential,” “opamp (operational amplifier),” and “gain-boosting.” Terms and basic concepts like these are apparent from prior art documents, e.g. text books such as “Design of Analog CMOS Integrated Circuits” by Behzad Razavi, McGraw-Hill (ISBN 0-07-118839-8), and thus will not be explained in detail here.
An amplifier is an apparatus widely used in a receiver for receiving an input voltage VI and outputting an output voltage VO such thatVO≈G·VI  (1)
Here, G is a gain of the amplifier.
In many applications, the input voltage VI contains a noise component that is deterministic and can be accurately estimated. For instance, in a full-duplex transceiver comprising a transmitter and a receiver, wherein transmission of a first signal by the transmitter and reception of a second signal by the receiver occur concurrently, a part of the first signal leaks from the transmitter into the receiver and combines with the second signal to form a third signal. The part of the first signal that leaks into the receiver and combines with the second signal is often referred to as an “echo.” The third signal, instead of the second signal, is what the receiver actually receives in the presence of the echo. Although the echo is a noise component within the third signal, as far as the receiver is concerned, it is not a random noise. Instead, the echo is a leakage of the first signal from the transmitter, and therefore correlates well with the first signal, which is readily known by the transmitter. By examining a correlation between the third signal and the first signal, the echo can be estimated. The echo is thus a deterministic noise that can be estimated, and must be cancelled by the receiver to assure good performance for the receiver. In U.S. Pat. No. 7,269,211, Lin et at teaches a method for echo reduction, wherein amplification and echo cancellation (which is a special case of deterministic noise cancellation) are two separate functions and fulfilled by two separate functional blocks of the receiver.
What is desired and disclosed is: an apparatus that fulfills amplification and deterministic noise cancellation at the same time, and method thereof.